Emission gas treatment method and emission gas treatment apparatus

ABSTRACT

An emission gas treatment apparatus recovers a recycle feed containing boron from emission gas discharged by a glass melting furnace. The apparatus includes a collection device for collecting a component containing boron from the emission gas by a wet process to obtain a collected liquid, a first filter for separating the collected liquid into a solid and a liquid, and an ion-exchange resin for forming a boron solution by removing an impurity from an extracted liquid obtained in the first filter. The apparatus also includes a mixing tank for mixing an extracted solid obtained in the first filter in the boron solution to form an extracted solid-containing solution, a second filter for separating the extracted solid-containing solution into a solid and a liquid, and a vacuum dryer for recovering the recycle feed from an extracted solid obtained in the second filter.

TECHNICAL FIELD

The present invention relates to a technology for recovering a recyclefeed from emission gas discharged by a glass melting furnace for meltinga glass raw material.

BACKGROUND ART

In a glass melting furnace, molten glass is produced by heating a glassraw material in a powder or particle form with a burner flame or thelike. This molten glass is formed into various glass products throughpredetermined forming steps such as pressing and blowing.

In this case, emission gas generated from the glass melting furnacecontains apart of components of the glass raw material in a gaseous orsmall-sized solid form. Therefore, the emission gas also contains agreat amount of components which can be recycled as a glass rawmaterial. Thus, the recovery of a recycle feed from the emission gas canalso contribute to saving of a glass raw material. Further, environmentcan be simultaneously taken into consideration.

However, when an attempt is made to recover a recycle feed from theemission gas, the recycle feed contains a great amount of componentswhich has an adverse effect on the quality of glass due to fuel for aburner flame and impurities contained in the glass raw material.Therefore, it is actually difficult to use a recycle feed recovered fromemission gas as a glass raw material. Herein, as the impurities whichhave an adverse effect on the quality of glass, for example, there aregiven a hydrosulfate and a halide, and the hydrosulfate causes thegeneration of air bubbles in glass.

For example, in Patent Literature 1, there is disclosed a method ofreducing a sulfur oxide which causes air bubbles from the emission gasand recovering a recycle feed which can be utilized as a glass rawmaterial by using fuel not substantially containing a sulfur componentas fuel for a burner flame and using a material whose content of asulfur component is also small correspondingly as a glass raw material.

CITATION LIST

Patent Literature 1: JP 2004-238236 A

SUMMARY OF INVENTION Technical Problem

In the case of borosilicate glass, when a glass raw material is meltedin a glass melting furnace, emission gas contains boron. Therefore, whenboron can be recovered as a recycle feed from the emission gas, therecycle feed can be used as a glass raw material with good quality.

However, when an attempt is made to recover boron from the emission gasby the method described in Patent Literature 1, the following problemmay occur. Specifically, even when fuel, a glass raw material, or thelike whose content of impurities is small is used, a hydrosulfate and ahalide being impurity components of the fuel, the glass raw material, orthe like cannot be removed completely. Therefore, the hydrosulfate andthe halide are recovered simultaneously to some degree as a recyclefeed, and boron cannot be recovered efficiently. Further in this case,when the recovery of a recycle feed in the emission gas is repeated, theconcentration of the hydrosulfate and the halide in the recycle feedincreases, which may serve as a factor for having an adverse effect onthe quality of glass.

It is a technical object of the present invention to recover boronefficiently from emission gas discharged by a glass melting furnace formelting a boron-containing glass raw material.

Solution to Problem

According to a first invention devised to achieve the above-mentionedobject, there is provided a emission gas treatment method for recoveringa recycle feed containing boron from emission gas discharged by a glassmelting furnace for melting a boron-containing glass raw material, theemission gas treatment method comprising: a collection step of obtaininga collected liquid by collecting a component containing boron from theemission gas by a wet process; a first separation step of separating thecollected liquid into a solid and a liquid; a solution formation step ofobtaining a boron solution by removing an impurity from an extractedliquid obtained in the first separation step; a mixing step of obtainingan extracted solid-containing solution by mixing an extracted solidobtained in the first separation step in the boron solution; a secondseparation step of separating the extracted solid-containing solutioninto a solid and a liquid; and a recovery step of recovering the recyclefeed from an extracted solid obtained in the second separation step.Note that, the term “boron” as used herein includes a boron compoundsuch as boric acid (the same applies to the following).

According to the above-mentioned configuration, boron not substantiallycontaining impurities such as a hydrosulfate and a halide can berecovered efficiently from the emission gas discharged by the glassmelting furnace for the following reason.

The collected liquid obtained in the collection step is separated into asolid and a liquid: an extracted solid and an extracted liquid in thefirst separation step. Of those, the extracted liquid is formed into aboron solution with impurities removed in the solution formation step.Boron has already been dissolved in the boron solution, and theconcentration of boron therein is high. Therefore, when the extractedsolid and the boron solution are mixed to form an extractedsolid-containing solution in the mixing step, boron in the extractedsolid is difficult to be dissolved in the extracted solid-containingsolution and remains as an undissolved substance. On the other hand,impurities (a hydrosulfate, a halide, etc.) other than boron in theextracted solid are soluble, and the concentration of the impurities inthe boron solution is low; therefore, the impurities are dissolvedeasily in the extracted solid-containing solution. Thus, when theextracted solid which is the undissolved substance is taken out byseparating the extracted solid-containing solution in such a dissolvedstate into a solid and a liquid in the second separation step, a recyclefeed containing boron whose content of impurities is very small can berecovered in the recovery step.

Herein, it is also conceivable to introduce water instead of the boronsolution and mix the extracted solid with water in the mixing step.However, in this case, not only the impurities in the extracted solidbut also most part of boron is dissolved in the water. Therefore, evenwhen the extracted solid-containing solution is separated into a solidand a liquid in the second separation step, most part of boron isrecovered as an extracted liquid and cannot be separated smoothly fromthe impurities. Thus, in the mixing step, as described above, it isimportant to mix the extracted solid with the boron solution so as tohave the above-mentioned actions and effects. Further, a boron solutionto be purified in a system is used, and hence it is not necessary toseparately introduce a boron solution from outside the system.

In the above-mentioned method, it is preferred that the solutionformation step comprise removing the impurity from the extracted liquidthrough use of an ion-exchange resin.

With this, boron in the extracted liquid can be recovered efficiently.That is, boron is unlikely to adsorb to ions due to its weak acidity andpasses through the ion-exchange resin. On the other hand, impuritycomponents (a hydrosulfate, a halide, etc.) other than boron are likelyto adsorb to ions due to their strong acidity and captured by theion-exchange resin. Thus, when the ion-exchange resin is used,impurities in the extracted liquid can be removed efficiently while thereduction amount of boron in the extracted liquid is reduced as much aspossible. As the ion-exchange resin, it is preferred to use a weaklybasic anion-exchange resin from the viewpoint of preventing boronadsorption.

In the above-mentioned method, it is preferred that the first separationstep and the second separation step comprise performing solid-liquidseparation by filtration.

With this, the solid-liquid separation can be performed easily andefficiently.

In the above-mentioned method, the emission gas treatment method mayfurther comprise supplying an extracted liquid obtained in the secondseparation step to the solution formation step. The solution formationstep may comprise obtaining the boron solution by removing an impurityfrom the extracted liquid obtained in the first separation step and fromthe extracted liquid obtained in the second separation step. Therecovery step may comprise recovering the recycle feed by drying theextracted solid obtained in the second separation step.

With this, the recycle feed can be recovered efficiently from a solidwithout wasting the extracted liquid generated in the second separationstep.

In the above-mentioned method, the emission gas treatment method mayfurther comprise: a second solution formation step of obtaining a boronsolution by removing an impurity from an extracted liquid obtained inthe second separation step; and a second mixing step of obtaining anextracted solid-containing solution by mixing the extracted solidobtained in the second separation step in the boron solution obtained inthe second solution formation step. The recovery step may compriserecovering the recycle feed by drying the extracted solid-containingsolution obtained in the second mixing step.

With this, the recycle feed can be recovered efficiently from a liquidwithout wasting the extracted liquid generated in the second separationstep.

According to a second invention devised to achieve the above-mentionedobject, there is provided a emission gas treatment method for recoveringa recycle feed containing boron from emission gas discharged by a glassmelting furnace for melting a boron-containing glass raw material, theemission gas treatment method comprising: a collection step of obtainingcollected powder by collecting a component containing boron from theemission gas by a dry process; a mixing step of obtaining a collectedpowder-containing solution by mixing the collected powder in a solution;a separation step of separating the collected powder-containing solutioninto a solid and a liquid; a solution formation step of obtaining aboron solution by removing an impurity from an extracted liquid obtainedin the separation step and supplying the boron solution as the solutionin the mixing step; and a recovery step of recovering the recycle feedfrom an extracted solid obtained in the separation step.

According to the above-mentioned configuration, the recovery rate ofboron can be enhanced efficiently while the recovery rate of impuritiessuch as a hydrosulfate and a halide is reduced as much as possible forthe following reason.

The collected powder obtained in the collection step is mixed with thesolution in the mixing step to form a collected powder-containingsolution. The collected powder-containing solution is separated into asolid and a liquid: an extracted solid and an extracted liquid in theseparation step. Of those, the extracted liquid is formed into a boronsolution with impurities removed in the solution formation step, andthereafter the boron solution is returned as the above-mentionedsolution in the mixing step. Therefore, in the mixing step, thecollected powder and the boron solution are mixed; however, theconcentration of boron in the boron solution has already been high, andhence boron in the collected powder is unlikely to be dissolved andremains as an undissolved substance in the solution. On the other hand,impurities (a hydrosulfate, a halide, etc.) other than boron in thecollected powder are dissolved easily due to the low concentrationthereof in the boron solution. Thus, when the collectedpowder-containing solution in such a dissolved state is separated into asolid and a liquid, and an extracted solid which is the undissolvedsubstance is taken out in the separation step, a recycle feed containingboron whose content of impurities is very small can be recovered in therecovery step.

In the above-mentioned method, the solution formation step may compriseremoving the impurity from the extracted liquid through use of anion-exchange resin. Further, the separation step may comprise performingsolid-liquid separation by filtration.

According to a third invention devised to achieve the above-mentionedobject, there is provided a emission gas treatment apparatus forrecovering a recycle feed containing boron from emission gas dischargedby a glass melting furnace for melting a boron-containing glass rawmaterial, the emission gas treatment apparatus comprising: collectionmeans for collecting a component containing boron from the emission gasby a wet process to obtain a collected liquid; first separation meansfor separating the collected liquid into a solid and a liquid; solutionformation means for forming a boron solution by removing an impurityfrom an extracted liquid obtained in the first separation means; amixing tank for mixing an extracted solid obtained in the firstseparation means in the boron solution to form an extractedsolid-containing solution; second separation means for separating theextracted solid-containing solution into a solid and a liquid to takeout an undissolved substance in the extracted solid-containing solution;and recovery means for recovering the recycle feed from an extractedsolid obtained in the second separation means.

According to the above-mentioned configuration, the action and effectsimilar to those of the first invention which has already been describedcan be exhibited.

According to a fourth invention devised to achieve the above-mentionedobject, there is provided a emission gas treatment apparatus forrecovering a recycle feed containing boron from emission gas dischargedby a glass melting furnace for melting a boron-containing glass rawmaterial, the emission gas treatment device comprising: collection meansfor collecting a component containing boron from the emission gas by adry process to obtain collected powder; a mixing tank for mixing thecollected powder in a solution to form a collected powder-containingsolution; separation means for separating the collectedpowder-containing solution into a solid and a liquid to take out anundissolved substance in the collected powder-containing solution;solution formation means for forming a boron solution by removing animpurity from an extracted liquid obtained in the separation means andsupplying the boron solution as the solution in the mixing tank; andrecovery means for recovering the recycle feed from an extracted solidobtained in the separation means.

According to the above-mentioned configuration, the action and effectsimilar to those of the second invention which has already beendescribed can be exhibited.

Advantageous Effects of Invention

As described above, according to one embodiment of the presentinvention, it is possible to recover boron whose content of impuritiessuch as a hydrosulfate and a halide is small from the emission gasdischarged by the glass melting furnace for melting the boron-containingglass raw material.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a glass melting facility in which aemission gas treatment apparatus according to a first embodiment of thepresent invention is incorporated.

FIG. 2 is a diagram illustrating a glass melting facility in which aemission gas treatment apparatus according to a second embodiment of thepresent invention is incorporated.

FIG. 3 is a diagram illustrating a glass melting facility in which aemission gas treatment apparatus according to a third embodiment of thepresent invention is incorporated.

DESCRIPTION OF EMBODIMENTS

Now, embodiments of the present invention are described with referenceto the attached drawings.

First Embodiment

FIG. 1 is a diagram illustrating a glass melting facility in which aemission gas treatment apparatus according to a first embodiment of thepresent invention is incorporated. The glass melting facility producesmolten glass to be formed into borosilicate glass by heating aboron-containing glass raw material (hereinafter simply referred to as“glass raw material”) “a” prepared so as to have an intended glasscomposition with a burner flame in a glass melting furnace 1. It ispreferred to use, for example, LPG or LNG whose content of a sulfurcomponent is small as fuel for the burner flame. Further, it ispreferred to use the glass raw material “a” whose content of a sulfurcomponent is also small.

Emission gas “b” generated from the glass melting furnace 1 contains asmall-sized solid and a vaporized substance derived from the glass rawmaterial “a” and the fuel for the burner flame. Therefore, the emissiongas “b” contains a hydrosulfate and a halide derived from the impuritiesof the glass raw material “a” and the fuel besides boron which is auseful component.

The emission gas “b” is first introduced to collection means 2. In thecollection means 2, the emission gas “b” is cooled to, for example, 60°C. to 70° C., and boron contained in a vaporized state in the emissiongas “b” is crystallized out.

In this embodiment, the collection means 2 is wet-type collection meanscomprising a spray tower 3 and a wet-type electric dust collector 4.Note that, the collection means 2 is not particularly limited as long asit can collect a boron component from emission gas by a wet process, andfor example, a scrubber may be used.

Components (a small-sized solid and a vaporized substance) containingboron contained in the emission gas “b” is collected as a collectedliquid “c” by being brought into contact with water sprayed in the spraytower 3. Further, a component “e” containing boron having passed throughthe spray tower 3 is also collected as the collected liquid “c” by beingbrought into contact with water in the wet-type electric dust collector4. The emission gas “d” purified while passing through the wet-typeelectric dust collector 4 is released into the atmosphere from a chimneypipe 5. Note that, the wet-type electric dust collector 4 plays anauxiliary role of the spray tower 3, and hence may be omitted.

The collected liquid “c” collected in the spray tower 3 and the wet-typeelectric dust collector 4 is introduced to a neutralization tank 6. Inthe neutralization tank 6, an alkali component such as hydrated lime “f”is added to the collected liquid “c” to neutralize the collected liquid“c” exhibiting an acidity. This prevents a tubing and the like frombeing corroded with an acid in subsequent steps and lowers thesolubility of boron in the collected liquid “c” to enhance the recoveryefficiency thereof. Note that, the neutralization tank 6 may be omitted.

Herein, the collected liquid “c” is subjected to neutralizationtreatment so that the concentration (pH) of hydrogen ions becomes weaklyalkaline, for example, 7.5 to 12.0, more preferably 8.0 to 10.0.

A collected liquid “g” neutralized in the neutralization tank 6 isintroduced to a first filter 7 serving as solid-liquid separation means.In the first filter 7, the collected liquid “g” is separated into asolid and a liquid: an extracted solid (filter cake) “k” and anextracted liquid (filtrate) “h”. Note that, the extracted solid “k”contains a liquid component of about 10% to 20%, and the liquidcomponent contains a great amount of impurities.

Examples of the first filter 7 include filter pressing, centrifugation,and vacuum filtration.

The extracted liquid “h” obtained in the first filter 7 is introduced toan ion-exchange resin 8 serving as solution formation means. Theextracted liquid “h” contains a hydrosulfate, a halide, calcium, andboron. In the ion-exchange resin 8, impurities (for example, ahydrosulfate, a halide, etc.) in the extracted liquid “h” are removed.More specifically, boron (mainly, boric acid) in the extracted liquid“h” is unlikely to adsorb to ions due to its weak acidity and passesthrough the ion-exchange resin 8. On the other hand, impurities “i”other than boron in the extracted liquid “h” are likely to adsorb toions due to its strong acidity. The impurities “i” are captured by theion-exchange resin 8 and cannot pass through the ion-exchange resin 8.Thus, when the extracted liquid “h” is caused to pass through theion-exchange resin 8, a boron solution “j” with the impurities “i”removed is formed. Note that, for example, a reverse osmosis membrane orthe like may be used as the solution formation means, but anion-exchange resin is preferably used because the recovery rate of boronis degraded when the reverse osmosis membrane or the like is used.Further, calcium can be used as a glass raw material, and hence there isno problem even when calcium is mixed in boron.

Herein, it is preferred in the boron solution “j” that boron be in asaturated state or close to a saturated state. In other words, it ispreferred that the boron solution “j” be a high-concentration solutionof boron. The concentration of boron in the boron solution “j” is, forexample, preferably 0.1% to 0.8%, more preferably 0.3% to 0.6%.

On the other hand, the extracted solid “k” obtained in the first filter7 is introduced to a mixing tank 9. In the mixing tank 9, the boronsolution “j” formed with the ion-exchange resin 8 is also introduced,and the extracted solid “k” and the boron solution “j” are mixed in themixing tank 9 to form an extracted solid-containing solution “l”. Inthis case, the concentration of boron in the boron solution “j” hasalready been high, and hence boron in the extracted solid “k” isunlikely to be dissolved and remains as an undissolved substance in theextracted solid-containing solution “l”. In contrast, the concentrationof impurities in the boron solution “j” is low, and hence the impuritiesin the extracted solid “k” are easily dissolved in the extractedsolid-containing solution “l”.

The extracted solid-containing solution “l” obtained in the mixing tank9, which exhibits such a dissolved state, is introduced to a secondfilter 10. In the second filter 10, the extracted solid-containingsolution “l” is separated into a solid and a liquid: an extracted solid“n” and an extracted liquid “m”. Note that, the extracted solid “n”contains a liquid component of about 10% to 20%, and the liquidcomponent contains almost no impurities.

Examples of the second filter 10 include filter pressing,centrifugation, and vacuum filtration.

The extracted liquid “m” obtained in the second filter 10 is introducedto the ion-exchange resin 8. That is, in this embodiment, the impurities“i” are removed from the extracted liquid “h” obtained in the firstfilter 7 and the extracted liquid “m” obtained in the second filter 10with the ion-exchange resin 8 to form the boron solution “j” to besupplied to the mixing tank 9.

On the other hand, the extracted solid “n” obtained in the second filter10 is introduced to a vacuum dryer 11 serving as recovery means. In thevacuum drier 11, moisture contained in the extracted solid “n” isremoved by drying to form a powdery recycle feed “o”, and the recyclefeed “o” is supplied to the glass melting furnace 1 together with theglass raw material “a”. In this case, the extracted solid “n” to besubjected to vacuum drying is an undissolved substance containing boronin the extracted solid-containing solution “l” as described above.Therefore, when moisture is removed from the extracted solid “n” bydrying, boron whose content of impurities is small can be recovered.Boron is generally recovered as boric acid. Further, calcium may berecovered simultaneously with boron. On the other hand, the impurities“i” in the emission gas “b” are successively discharged out of a systemwith the ion-exchange resin 8. Therefore, even when recycling isrepeated, the impurities “i” can be prevented without fail from beingcontained in the recycle feed “o” in a concentrated state.

The recovery means is not limited to the vacuum dryer 11, and in thisembodiment, the recovery means is not particularly limited as long as itis means capable for removing moisture from a solid by drying. Forexample, the recovery means may also be a rotary dryer or a band dryer.

Next, the operation of the glass melting facility in which the emissiongas treatment apparatus configured as described above is incorporated isdescribed.

First, the glass raw material “a” is supplied into the glass meltingfurnace 1 to produce molten glass. From the emission gas “b” generatedat this time, a component containing boron is collected as the collectedliquid “c” by the spray tower 3 and the wet-type electric dust collector4, and the purified emission gas “d” is released to the atmosphere fromthe chimney pipe 5.

The collected liquid “c” is neutralized in the neutralization tank 6 andseparated into a solid and a liquid by the first filter 7. The extractedliquid “h” obtained through separation into a solid and a liquid isintroduced to the ion-exchange resin 8 and has the impurities “i”removed therefrom to form the boron solution “j”. Then, the boronsolution “j” is introduced to the mixing tank 9. The impurities “i”removed with the ion-exchange resin 8 are released out of the system.

On the other hand, the extracted solid “k” obtained through separationinto a solid and a liquid is introduced to the mixing tank 9 togetherwith the boron solution “j”. In the mixing tank 9, the extracted solid“k” and the boron solution “j” are mixed, and the extractedsolid-containing solution “l” is formed. In the extractedsolid-containing solution “l”, boron in the extracted solid “k” remainsas an undissolved substance, and impurities other than boron in theextracted solid “k” are dissolved.

The extracted solid-containing solution “l” exhibiting such a dissolvedstate is separated into a solid and a liquid by the second filter 10.The extracted liquid “m” obtained through separation into a solid and aliquid is introduced to the ion-exchange resin 8 to be a material forthe boron solution “j”.

On the other hand, the extracted solid “n” obtained through separationinto a solid and a liquid has moisture removed by drying with the vacuumdryer 11 to form the recycle feed “o” containing boron whose content ofimpurities is small.

Note that, in the case of forming a recycle feed by the method of PatentLiterature 1, the impurities in the recycle feed contain, for example,about 2,000 ppm of a hydrosulfate and about 50,000 ppm of a halide,whereas in the case of forming a recycle feed by the configuration ofthe first embodiment, the amounts of a hydrosulfate and a halide in theimpurities of the recycle feed can be greatly reduced to about 100 ppmand 100 ppm, respectively.

Second Embodiment

FIG. 2 is a diagram illustrating a glass melting facility in which aemission gas treatment apparatus according to a second embodiment of thepresent invention is incorporated. The second embodiment is differentfrom the first embodiment in a drying method in a recovery step forobtaining a recycle feed. Note that, like elements are denoted with likereference symbols, and the detailed description thereof is omitted.

That is, the second embodiment is different from the first embodiment inthat a recycle feed is formed from a solid in the first embodiment,while a recycle feed is formed from a liquid in the second embodiment.Note that, the procedure up to the second filter 10 in FIG. 2 is thesame as that of the first embodiment, and hence the subsequent steps aredescribed.

That is, the extracted solid-containing solution “l” obtained in thefirst mixing tank (corresponding to the mixing tank of the firstembodiment) 9 is separated into a solid and a liquid by the secondfilter 10, and an extracted liquid “a2” is introduced to a secondion-exchange resin 21. In the second ion-exchange resin 21, impurities“b2” are removed from the extracted liquid “a2” to form a boron solution“c2”, and the boron solution “c2” is introduced to a second mixing tank22.

On the other hand, an extracted solid “d2” obtained in the second dryer10 is introduced to the secondmixing tank 22 together with the boronsolution “c2”. In the second mixing tank 22, the extracted solid “d2”and the boron solution “c2” are mixed to form an extractedsolid-containing solution “e2”. The extracted solid-containing solution“e2” is obtained by mixing the extracted solid “d2” which is anundissolved substance containing boron with high purity with the boronsolution “c2”, and hence the solution hardly contains impurities otherthan boron.

The extracted solid-containing solution “e2” is introduced to a spraydryer 23. In the spray dryer 23, the extracted solid-containing solution“e2” is sprayed into hot air, and moisture in the extractedsolid-containing solution “e2” is removed by drying with heat of the hotair. In this case, the extracted solid-containing solution “e2” to bedried is also a liquid hardly containing components other than boron, asdescribed above. Therefore, when moisture is removed from the extractedsolid-containing solution “e2” by drying, a recycle feed “f2” containingboron whose content of impurities is small can be recovered.

Note that, gas “g2” generated by the spray dryer 23 is supplied to thespray tower 3. As the hot air to be supplied into the spray dryer 23,for example, hot air generated in the glass melting furnace 1 is used.Further, a drum dryer, a CD dryer, or the like can be used instead ofthe spray dryer 23.

Even in the case of forming a recycle feed by the configuration of thesecond embodiment, the amounts of a hydrosulfate and a halide in theimpurities of the recycle feed can be suppressed to about 100 ppm andabout 100 ppm, respectively.

Third Embodiment

FIG. 3 is a diagram illustrating a glass melting facility in which aemission gas treatment apparatus according to a third embodiment of thepresent invention is incorporated. The third embodiment is differentfrom the first and second embodiments in that a component containingboron is collected from emission gas by a dry process. Note that, likeelements are denoted with like reference symbols, and the detaileddescription thereof is omitted.

That is, in this embodiment, collection means 31 comprises a coolingtower 32 and a bag filter 33. The emission gas “b” is cooled by beingbrought into contact with wind (air) of the cooling tower 32, and thecooled emission gas “a3” is introduced to the bag filter 33. In the bagfilter 33, solid components (a small-sized solid and a gaseous substancecrystallized by being cooled) in the cooled emission gas “a3” arecollected as collected powder “b3”. The purified emission gas “c3”having passed through the bag filter 33 is released to the atmospherefrom the chimney pipe 5. Note that, a dry-type electric dust collectormay be used instead of the bag filter 33.

The collected powder “b3” is introduced to a mixing tank 34. In themixing tank 34, the collected powder “b3” and a solution are mixed toform a collected powder-containing solution “e3”. Further, an alkalicomponent made of hydrated lime “d3” or the like is added to the mixingtank 34, and thus the collected powder-containing solution “e3” issubjected to neutralization treatment. Note that, as the solution, wateror a boron solution supplied from outside is used only at the beginning(in the initial period) of an operation. Further, the neutralizationtreatment may be omitted.

The collected powder-containing solution “e3” obtained in the mixingtank 34 is introduced to a filter 35. In the filter 35, the collectedpowder-containing solution “e3” is separated into a solid and a liquid.

An extracted liquid “f3” obtained in the filter 35 is introduced to anion-exchange resin 36. In the ion-exchange resin 36, impurities “g3” areremoved from the extracted liquid “f3” to form a boron solution “h3”.The boron solution “h3” is returned as the solution of the mixing tank34. After the boron solution “h3” is supplied to the mixing tank 34,boron in the collected powder “b3” remains as an undissolved substancein the collected powder-containing solution “e3”, and impurities in thecollected powder “b3” are dissolved therein for the reason described inthe first embodiment.

On the other hand, an extracted solid “i3” obtained in the filter 35 isintroduced to a vacuum dryer 37. The extracted solid “i3” to be dried isan undissolved substance containing boron with high purity. Therefore,when moisture contained in the extracted solid “i3” is removed by dryingin the vacuum dryer 35, boron whose content of impurities is small canbe recovered as a recycle feed “j3”.

Even in the case of forming a recycle feed by the configuration of thethird embodiment, the amounts of a hydrosulfate and a halide in theimpurities of the recycle feed can be suppressed to about 100 ppm and100 ppm, respectively.

REFERENCE SIGNS LIST

-   1 glass melting furnace-   2 collection means-   3 spray tower-   4 wet-type electric dust collector-   5 chimney pipe-   6 neutralization tank-   7 first filter-   8 ion-exchange resin-   9 mixing tank-   10 second filter-   11 vacuum dryer

The invention claimed is:
 1. A emission gas treatment method forrecovering a recycle feed containing boron from emission gas dischargedby a glass melting furnace for melting a boron-containing glass rawmaterial, the emission gas treatment method comprising: a collectionstep of obtaining collected powder by collecting a component containingboron from the emission gas by a dry process; a mixing step of obtaininga collected powder-containing solution by mixing the collected powder ina solution; a separation step of separating the collectedpowder-containing solution into a solid and a liquid; a solutionformation step of obtaining a boron solution by removing an impurityfrom an extracted liquid obtained in the separation step and supplyingthe boron solution as the solution in the mixing step; and a recoverystep of recovering the recycle feed from an extracted solid obtained inthe separation step.
 2. The emission gas treatment method according toclaim 1, wherein the solution formation step comprises removing theimpurity from the extracted liquid through use of an ion-exchange resin.3. The emission gas treatment method according to claim 1, wherein theseparation step comprises performing solid-liquid separation byfiltration.
 4. A emission gas treatment apparatus for recovering arecycle feed containing boron from emission gas discharged by a glassmelting furnace for melting a boron-containing glass raw material, theemission gas treatment apparatus comprising: collection means forcollecting a component containing boron from the emission gas by a dryprocess to obtain collected powder; a mixing tank for mixing thecollected powder in a solution to form a collected powder-containingsolution; separation means for separating the collectedpowder-containing solution into a solid and a liquid; solution formationmeans for forming a boron solution by removing an impurity from anextracted liquid obtained in the separation means and supplying theboron solution as the solution in the mixing tank; and recovery meansfor recovering the recycle feed from an extracted solid obtained in theseparation means.
 5. The emission gas treatment method according toclaim 2, wherein the separation step comprises performing solid-liquidseparation by filtration.